Radiation therapy is known in the art. Generally speaking, such therapy typically involves exposing an unwanted volume on or within a patient's body to high-energy photonic radiation (such as, but not limited to, x-rays). This radiation often serves to destroy the irradiated cellular material and hence reduce or eliminate the unwanted volume. In many cases such radiation is periodically administered over time (days, weeks, or months) in a series of discrete treatment sessions.
Many treatment plans provide for exposing the patient's target volume to such radiation from a number of different directions. Arc therapy, for example, comprises one such approach. In such a case it often becomes necessary to adjust the delivery of the radiation during such a treatment in order to avoid collateral harm and/or to best ensure the desired dosage distribution.
Heavy particles are sometimes also used for a similar purpose, albeit often in a dissimilar way. Heavy particles (such as protons, heavy ions, antiprotons, and pions) behave considerably different than the photons of more traditional radiation sources such as x-rays. As a result, it is not possible to simply exchange a heavy-particle source for a photonic radiation source in many treatment systems (such as, for example, an arc therapy system) as the desired results of such treatment will not be inherently met. Instead, an inadequate (or otherwise inappropriate) dosage of the treatment volume and/or undesired (and avoidable) harm to other portions of the patient's body can result.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.